Anionic additives soluble in water and in solvents

ABSTRACT

The invention relates to anionically modified copolymers that can be obtained by the polymerization of monomers (A), (B), (C) and (D) in order to obtain non-ionic copolymers comprising reactive terminal OH groups, and subsequent reaction of the terminal OH groups to form anionic end groups, where A) is a monomer of formula (I) wherein A is C2-C4 alkylene and B is a C2-C4 alkylene different from A, and R is hydrogen or methyl; (B) is a monomer of formula (II) wherein D is C3 alkylene, R is hydrogen or methyl, and o is a number between 2 and 500; (C) is an ethylenically unsaturated monomer containing an aromatic group; and (D) is an ethylenically unsaturated monomer containing an alkyl radical.

The present invention relates to novel anionic copolymers, which areused as dispersants for water- and solventborne pigment formulations,and to a process for producing these copolymers.

Dispersing pigments in liquid media typically requires dispersants.Dispersants, augmented by suitable surfactants, also known as wetters,act as surface-active agents in promoting the wetting of the pigments tobe dispersed, and facilitate the deconstruction of agglomerates andaggregates when producing pigment dispersions, which is generallyaccomplished with the aid of a grinding operation. Dispersants can be ofanionic, cationic, amphoteric or neutral structure. They can be of lowmolecular weight, or represent high molecular weight polymers whichconstitute a random, alternating, blocklike, comblike or star-shapedarchitecture of the polymerized monomers. Examples of where dispersantsare of particular commercial importance are the dispersing of pigmentsin the manufacture of pigment concentrates (used for coloration ofemulsion and varnish colors, paints, coatings and printing inks) andalso the coloration of paper, cardboard and textiles. Lately, interesthas focused on the search for dispersants and additives which, followinga drying operation performed on the liquid dispersion, ensure rapiddissolving of the dry powder or granulate in the application medium.Comb polymers can be useful here.

Comb polymers are usually prepared using macromonomers based onmono(meth)acrylic esters as comonomers, and they differ from otherpolymeric dispersants in that they have a clearly ordered structurewherein hydrophobicity and hydrophilicity, or polarity, can beapportioned between the main chains and the side chains.

EP 1 293 523 describes a dispersant which is a polymer which has aweight average molecular weight of about 5000 to 100 000 and comprises20% to 80% by weight of a hydrophilic backbone and 80% to 20% by weightof macromonomeric side chains. The backbone consists of 70% to 98% byweight, based on the weight of the backbone, of polymerizedethylenically unsaturated monomers free of any carboxyl groups, and also2% to 30% by weight of polymerized ethylenically unsaturated monomersbearing a carboxyl group, wherein at least 10% of the carboxyl groupsare neutralized with an amine or an inorganic base. The backbone ishydrophilic in comparison to the side chains. The side chains consist ofmacromonomers of polymerized ethylenically unsaturated monomers.

EP 1 081 169 describes branched polymers derived from the followingmixture of monomers:

-   (A) 50% to 93% by weight of at least one ethylenically unsaturated    monomer,-   (B) 2% to 25% by weight of at least one ethylenically unsaturated    macromonomer having a molecular weight of 1000 to 20 000, and-   (C) 5% to 25% by weight of at least one polymerizable imidazole    derivative.

EP 1 562 696 describes polymeric dispersants synthesized, in aqueousemulsion polymerization, using macromonomers consisting of polyalkyleneglycol mono(meth)acrylates. The main chain of the polymer must containethylenically unsaturated monomers having at least one amino group.

DE 10 2005 019 384 describes comb polymers which are synthesized fromethylenically unsaturated monomers such as alkyl(meth)acrylates andaryl(meth)acrylates in combination with a pure polyethylene glycolmono(meth)acrylate, and are used as dispersants.

EP 1 323 789 describes comb-type polymers which contain polyalkyleneoxide mono(meth)acrylate units, yet are not water soluble. An object isto provide aqueous inks. EP 1 491 598 is similar in that it containspolyalkylene oxide mono(meth)acrylate units and salt-forming monomers;the polymers are used for aqueous inks.

The patents cited describe the state of the art of providing comb-shapedor block-forming polymers as dispersants. However, the dried powders orgranulates are easily dispersed in an aqueous system only or in asolvent-containing system only.

No invention described to date provides dispersants capable ofeffectively stabilizing aqueous pigment dispersions which aresubsequently readily dryable, for example by spray drying, to produce apowder or granulate capable of easy dispersion in aqueous andsolvent-containing systems alike, with rapid and high development ofcolor strength. The decisive advantage here is the universaldispersibility of the powder or granulate in both aqueous andsolvent-containing systems.

It has now been found that, surprisingly, specific anionic combcopolymers, prepared by means of macromonomers composed ofpolyethylene/polypropylene glycol mono(meth)acrylic esters, achieve theobject described, viz., universal dispersibility.

The present invention accordingly provides anionically modifiedcopolymers obtainable by polymerization of monomers (A), (B), (C) and(D) to obtain nonionic copolymers having reactive terminal OH groups,and subsequent conversion of the terminal OH groups to anionic endgroups, for example to sulfuric monoesters, where

(A) is a monomer of formula (I)

where

-   A represents C₂-C₄-alkylene,-   B represents a C₂-C₄-alkylene other than A,-   R represents hydrogen or methyl,-   m is from 1 to 500, preferably 1 to 50;-   n is from 1 to 500, preferably 1 to 50,-   and the sum total of m+n is from 2 to 1000;    (B) is a monomer of formula (II)

where

-   D represents C₃-alkylene,-   R represents hydrogen or methyl,-   o is from 2 to 500, preferably 2 to 100, particularly 2 to 50,    particularly preferably 5 to 25;    (C) is an ethylenically unsaturated monomer which contains an    aromatic group; and    (D) is an ethylenically unsaturated monomer which contains an alkyl    radical.

The copolymer of the present invention has customary terminal groupswhich are formed by the initiation of the free-radical polymerization orby chain transfer reactions or by chain termination reactions, forexample a proton, a group derived from a free-radical initiator or asulfur-containing group derived from a chain transfer reagent.

The anionic end groups can be sulfates, carboxylates or phosphates.

The molar fraction of the monomers is preferably 0.1 to 90% for monomer(A), 0.1 to 90% for monomer (B), 0.1 to 90% for monomer (C) and 0.1 to90% for monomer (D), the molar fractions summing to 100%.

It is particularly preferable for the molar fraction of the monomers tobe 0.1 to 70% for monomer (A), 10 to 80% for monomer (B), 0.1 to 50% formonomer (C) and 0.1 to 50% for monomer (D).

The alkylene oxide units (A-O)_(m) and (B—O)_(n) of monomer (A) can bepresent either in a random arrangement or, as in the case of a preferredembodiment, in a blocklike arrangement.

In one preferred embodiment, (A-O)_(m) represents propylene oxide unitsand (B—O)_(n) represents ethylene oxide units, or (A-O)_(m) representsethylene oxide units and (B—O)_(n) represents propylene oxide units, andthe molar fraction of ethylene oxide units is preferably 50 to 98%, morepreferably 60 to 95% and even more preferably 70 to 95%, based on thesum total (100%) of ethylene oxide and propylene oxide units.

The sum total of the alkylene oxide units can in principle be n+m=2 to1000, although 2 to 500 is preferred, 2 to 100 is particularly preferredand 5 to 50 is even more particularly preferred.

Preferred monomers (C) can be described by the formula (IIIa) or (IIIb):

where

-   X_(a) represents an aromatic or araliphatic radical having 3 to 30    carbon atoms which optionally contains one or more, e.g., 1, 2 or 3,    of the heteroatoms N, O and S,-   Z_(a) represents H or (C₁-C₄)-alkyl,-   Z_(b) represents H or (C₁-C₄)-alkyl, and-   Z_(c) represents H or (C₁-C₄)-alkyl;

where

-   R¹ represents hydrogen or methyl,-   X_(b) represents an aromatic or araliphatic radical having 3 to 30    carbon atoms which optionally contains one or more, e.g., 1, 2, or    3, of the heteroatoms N, O und S,-   W_(a) represents oxygen or an NH group.

Useful monomers (C) include for example the following esters and amidesof acrylic acid and methacrylic acid: phenyl, benzyl, tolyl,2-phenoxyethyl, phenethyl. Further monomers (C) are vinylaromaticmonomers such as styrene and its derivatives, such as vinyltoluene andalpha-methylstyrene for example. The aromatic unit may also compriseheteroaromatics, as in 1-vinylimidazole for example.

Particularly preferred monomers (C) can be: styrene, 1-vinylimidazole,benzyl methacrylate, 2-phenoxyethyl methacrylate and phenethylmethacrylate.

Preferred monomers (D) can be described by formula (IV):

where

-   R² represents hydrogen or methyl,-   Y represents an aliphatic hydrocarbyl radical having 1 to 30 carbon    atoms, preferably 6 to 30, particularly 9 to 20 carbon atoms, which    may be linear or branched or else cyclic, and which may contain    heteroatoms O, N and/or S and may also be unsaturated,-   W_(b) represents oxygen or an NH group.

Monomers (D) include for example the following esters and amides ofacrylic acid and methacrylic acid: methyl, ethyl, propyl, isopropyl,n-butyl, isobutyl, t-butyl, pentyl, hexyl, 2-ethylhexyl,3,3-dimethylbutyl, heptyl, octyl, isooctyl, nonyl, lauryl, cetyl,stearyl, behenyl, cyclohexyl, trimethylcyclohexyl, t-butylcyclohexyl,bornyl, isobornyl, adamantyl, (2,2-dimethyl-1-methyl)propyl,cyclopentyl, 4-ethyl-cyclohexyl, 2-ethoxyethyl, tetrahydrofurfuryl andtetrahydropyranyl.

Preferred monomers (D) are the following alkyl esters and alkylamides ofacrylic acid and methacrylic acid: methyl, ethyl, propyl, butyl,isobutyl, 2-ethoxyethyl, myristyl, octadecyl, more preferably2-ethylhexyl and lauryl.

The copolymers of the present invention have a molecular weight of 10³g/mol to 10⁹ g/mol, more preferably of 10³ to 10⁷ g/mol and even morepreferably of 10³ to 10⁵ g/mol.

The copolymers of the present invention can be produced by means offree-radical polymerization. The polymerization reaction can be carriedout as a continuous operation, as a batch operation or as asemi-continuous operation.

The polymerization reaction is advantageously conducted as aprecipitation polymerization, an emulsion polymerization, a solutionpolymerization, a bulk polymerization or a gel polymerization. Asolution polymerization is particularly advantageous for the performanceprofile of the copolymers of the present invention.

Useful solvents for the polymerization reaction include all organic orinorganic solvents which are very substantially inert with regard tofree-radical polymerization reactions, examples being ethyl acetate,n-butyl acetate or 1-methoxy-2-propyl acetate, and also alcohols suchas, for example, ethanol, i-propanol, n-butanol, 2-ethylhexanol or1-methoxy-2-propanol, and also diols such as ethylene glycol andpropylene glycol. It is similarly possible to use ketones such asacetone, butanone, pentanone, hexanone and methyl ethyl ketone, alkylesters of acetic, propionic and butyric acids such as for example ethylacetate, butyl acetate and amyl acetate, ethers such as tetrahydrofuran,diethyl ethers, and monoalkyl and dialkyl ethers of ethylene glycol andof polyethylene glycol. It is similarly possible to use aromaticsolvents such as, for example, toluene, xylene or higher-boilingalkylbenzenes. The use of solvent mixtures is likewise conceivable, inwhich case the choice of solvent or solvents depends on the planned useof the copolymer of the present invention. Preference is given to usingwater; lower alcohols; preferably methanol, ethanol, propanols, iso-,sec- and t-butanols, 2-ethylhexanol, butyl glycol and butyl diglycol,more preferably isopropanol, t-butanol, 2-ethylhexanol, butyl glycol andbutyl diglycol; hydrocarbons having 5 to 30 carbon atoms and mixturesand emulsions thereof.

The polymerization reaction is preferably carried out in the temperaturerange between 0 and 180° C., more preferably between 10 and 100° C., notonly at 1.0 atmospheric pressure but also under elevated or reducedpressure. If appropriate, the polymerization can also be carried outunder a protective gas atmosphere, preferably under nitrogen.

The polymerization can be induced using high-energy, electromagneticrays, mechanical energy or the customary, chemical polymerizationinitiators such as organic peroxides, for example benzoyl peroxide,tert-butyl hydroperoxide, methyl ethyl ketone peroxide, cumoyl peroxide,dilauroyl peroxide (DLP) or azo initiators, for exampleazoisobutyronitrile (AIBN), azobisamidopropyl hydrochloride (ABAH) and2,2′-azobis(2-methylbutyronitrile) (AMBN). Similarly useful areinorganic peroxy compounds, for example (NH₄)₂S₂O₈, K₂S₂O₈ or H₂O₂, ifappropriate in combination with reducing agents (for example sodiumhydrogensulfite, ascorbic acid, iron(II) sulfate) or redox systems whichcontain an aliphatic or aromatic sulfonic acid (for examplebenzenesulfonic acid, toluenesulfonic acid) as reducing component.

The customary molecular weight regulators are used. Suitable knownregulators include for example alcohols, such as methanol, ethanol,propanol, isopropanol, n-butanol, sec-butanol and amyl alcohols,aldehydes, ketones, alkylthiols, for example dodecylthiol andtert-dodecylthiol, thioglycolic acid, isooctyl thioglycolate and somehalogen compounds, for example carbon tetrachloride, chloroform andmethylene chloride.

Following the polymerization, the solvent is removed.

The nonionic polymer thus obtained now possesses, on the polyoxyalkyleneside chains, reactive hydroxyl functions which are next converted toanionic functionalities. Examples of anionic functionalities are SO₃M,CH₂COOM, PO₃M₂ or sulfosuccinate. M therein has the hereinbelow definedmeaning.

The anionic copolymers of the present invention can be described forexample by the formulae (V) or (VI):

The indices a, b, c and d indicate the molar fraction of the respectivemonomer (A), (B), (C) and (D), viz.:

a=0.001-0.9; b=0.001-0.9; c=0.001-0.9; d=0.001-0.9;

preferably a=0.001-0.7; b=0.01-0.8; c=0.001-0.5; d=0.001-0.5;

subject to the proviso that the sum total of a+b+c+d is equal to 1.

The remaining variables are as defined in formula (I), (II), (IIIa) and(IIIb).

In formulae (V) and (VI), Q represents SO₃, CH₂COO, PO₃M, or QM is

and M represents H, a metal cation, or an ammonium, e.g. Na, K, Ca, NH₄⁺, an alkylated ammonium ion, or a combination thereof (the asterisk *in the Markush formula indicates that there is a link to the polymer atthis site).

In the case of the sulfosuccinates, the nonionic copolymers are forexample initially esterified with maleic anhydride. Here theesterification can be carried out without solvent in that the reactioncan be carried out in the polymer melt under elevated temperature.Subsequently, the maleic monoester obtained is sulfonated. To this end,it is reacted for example with sodium sulfite or sodium pyrosulfite inan aqueous solution. The product obtained is the aqueous solution of thesulfosuccinate sodium salt.

The sulfate esters are prepared for example by reacting the nonioniccopolymers with sulfamic acid. This reaction takes place in a melt ofthe nonionic copolymer in the presence of sulfamic acid. The OH groupsof the copolymer are converted into sulfate esters, which are thenpresent as ammonium salt.

The terminal hydroxyl functions can be converted into the correspondingpolyether carboxylates by carboxymethylation, for example with sodiumchloroacetate.

The phosphoric esters are obtainable for example by reacting a melt ofthe nonionic copolymer with polyphosphoric acid or phosphorus pentoxide.This reaction may yield not only phosphoric monoesters but alsophosphoric diesters and triesters.

Since the conversion of the nonionic polymer to anionic functionalitiesis usually not quantitative, the product is usually a mixture ofconverted polymer (QM=SO₃M, CH₂COOM, PO₃M₂, sulfosuccinate) andunconverted polymer (QM=H). This mixture is practically impossible toresolve, and can be used as such for the purposes of the presentinvention.

The present invention further provides for the use of the anioniccopolymer of the present invention as a dispersant particularly forpigments and fillers, for example in the preparation of waterborne orsolventborne pigment concentrates which are used for coloration ofdispersion and varnish colors, paints, coatings and printing inks, andalso for coloration or printing of paper, cardboard and textiles.

Synthesis Prescription 1:

General Prescription for Polymerization:

A flask equipped with stirrer, reflux condenser, internal thermometerand nitrogen inlet is initially charged with monomer A, monomer B,monomer C, monomer D and the molecular weight regulator in solvent whilenitrogen is introduced, in the parts by weight indicated in the tableswhich follow. Then, the temperature is raised to 80° C. with stirringand a solution of the initiator is added during one hour by metering.The batch is subsequently further stirred at this temperature for 2hours, and then the solvent is removed under reduced pressure.

Synthesis Prescription 2:

General Synthesis Prescription for Converting the Polymers ObtainedAccording to Synthesis Prescription 1 to Anionic Copolymers Having EtherSulfate Groups on the Side Chains:

The copolymer is initially charged in a flask under nitrogen togetherwith sulfamic acid and urea. The initial charge is then heated to 100°C. for 4 hours with stirring. Then, the pH is adjusted to 6.5-7.5 with50% aqueous sodium hydroxide solution. NMR spectroscopy can be used toverify a degree of conversion of >95% to the corresponding sulfuricester ammonium salt.

Synthesis Prescription 3:

General Synthesis Prescription for Converting the Polymers ObtainedAccording to Synthesis Prescription 1 to Anionic Copolymers HavingSulfosuccinate Groups on the Side Chains:

The copolymer is initially charged to a flask under nitrogen. Then,maleic anhydride and sodium hydroxide are added and the batch is heatedwith stirring to a temperature of 75-85° C. At this temperature, thebatch is stirred for three hours and then admixed with aqueous sodiumsulfite solution (10% strength by weight) by metered addition. At 60 to70° C., the batch is stirred to complete the reaction and subsequentlyadjusted to pH 7 with 50% by weight aqueous sodium hydroxide solution.

The two tables which follow contain two-stage synthesis examples inwhich the polymer is initially prepared according to synthesisprescription 1 and then the anionic derivative of the polymer isprepared according to synthesis prescription 2 or 3.

Example No. 1 2 3 4 5 6 7 8 9 10 Monomer A polyglycol 1 143.8 243.2 15.9polyglycol 2 137.3 106.9 polyglycol 3 93.0 242.5 polyglycol 4 0.4 154.0339.1 Monomer B polyglycol 6 183.1 277.8 186.0 285.0 231.0 102.7 121.356.5 69.5 227.3 Monomer C 1-vinylimidazole 13.1 0.4 styrene 19.0 8.0benzyl methacrylate 0.4 72.3 phenethyl methacrylate 0.4 66.02-phenoxyethyl methacrylate 0.4 93.6 Monomer D 2-ethylhexyl methacrylate110.5 lauryl methacrylate 46.5 52.2 stearyl methacrylate 94.2 0.4 0.4isobornyl methacrylate 0.4 26.9 vinyl neodecanoate 0.4 45.0 InitiatorAMBN 7.0 8.0 4.1 4.7 2.2 10.7 9.2 dibenzoyl peroxide 8.4 5.6 16.2Regulator dodecanethiol 7.0 6.6 4.1 12.6 4.6 2.1 10.6 9.1 ethylmercaptan 2.4 1.3 Solvent methyl ethyl ketone 600 600 methyl isobutylketone 600 600 600 isopropanol 600 600 600 600 600 M_(w) of polymerobtained 9800 14200 13500 17100 20500 16000 18900 17700 11300 19000derivatization of polymer to 2 3 2 2 3 3 2 3 2 2 synthesis prescriptionsulfamic acid 17.4 6.4 6.8 23.1 33.1 4.3 urea 0.3 0.1 0.1 0.4 0.6 0.1maleic anhydride 15.0 8.3 22.1 18.3 NaOH 0.9 0.5 1.32 1.09 sodiumsulfite solution 19.2 10.7 28.5 23.5 (10% in water) Example No. 11 12 1314 15 16 17 18 19 20 Monomer A polyglycol 1 155.4 212.7 57.3 polyglycol2 195.5 199.0 polyglycol 3 66.9 324.7 polyglycol 4 0.4 246.6 373.4Monomer B polyglycol 5 91.2 177.2 117.0 185.8 129.5 77.7 28.4 21.8 106.3114.7 Monomer C 1-vinylimidazole 23.8 styrene 27.1 0.4 12.8 benzylmethacrylate 78.2 phenethyl methacrylate 0.4 57.7 2-phenoxyethylmethacrylate 0.4 0.4 135.0 Monomer D 2-ethylhexyl methacrylate 198.6lauryl methacrylate 66.2 56.4 0.4 stearyl methacrylate 171.6 0.4isobornyl methacrylate 0.4 36.0 vinyl neodecanoate 0.4 64.9 InitiatorAMBN 10.0 13.5 7.6 5.5 2.4 11.7 14.2 dibenzoyl peroxide 15.3 9.0 17.5Regulator dodecanethiol 9.9 12.0 7.6 14.8 5.4 2.4 11.5 14.0 ethylmercaptan 4.1 2.2 Solvent methyl ethyl ketone 600 600 methyl isobutylketone 600 600 600 isopropanol 600 600 600 600 600 M_(w) of polymerobtained 7100 8200 14900 9500 17100 12600 22800 16000 9300 8400derivatization of polymer to 2 2 3 2 3 2 3 2 2 3 synthesis prescriptionsulfamic acid 12.4 24.1 25.3 21.2 — 17.8 28.9 urea 0.2 0.4 0.4 0.4 0.30.5 maleic anhydride 3.6 13.3 17.5 8.8 NaOH 0.2 0.8 1.0 0.5 sodiumsulfite solution 4.6 17.1 22.5 11.3 (10% in water)Composition of Monomer A:

-   Polyglycol 1 polyalkylene glycol monomethacrylic ester (formula (I),    m=n=3-4; (A-O) corresponds to [CH₂CH(CH₃)O)], (B—O) corresponds to    (CH₂CH₂O)), molar mass about 350 g/mol-   Polyglycol 2 polyalkylene glycol monomethacrylic ester (formula (I),    m=2, n=12-13; (A-O) corresponds to (CH₂CH(CH₃)O)), (B—O) corresponds    to (CH₂CH₂O)), molar mass about 750 g/mol-   Polyglycol 3 polyalkylene glycol monomethacrylic ester (formula (I),    m=2, n=17-19; (A-O) corresponds to (CH₂CH(CH₃)O)), (B—O) corresponds    to (CH₂CH₂O)), molar mass about 1000 g/mol-   Polyglycol 4 polyalkylene glycol monomethacrylic ester (formula (I),    m=2, n=40-42; (A-O) corresponds to (CH₂CH(CH₃)O)), (B—O) corresponds    to (CH₂CH₂O)), molar mass about 2000 g/mol    Composition of Monomer B:-   Polyglycol 5 polypropylene glycol monomethacrylic ester (formula    (II), o=4-5; (0-0) corresponds to [CH₂CH(CH₃)O)], molar mass about    350 g/mol-   Polyglycol 6 polypropylene glycol monomethacrylic ester (formula    (II), o=15-16; (D-0) corresponds to [CH₂CH(CH₃)O)], molar mass about    1000 g/mol    AMBN=2,2′-azobis(2-methylbutyronitrile)

USE EXAMPLE Production of a Pigment Formulation

The pigment, in the form alternatively of powder, granulate orpresscake, was pasted up in deionized water together with thedispersants and the other adjuvants and then homogenized andpredispersed using a dissolver (for example from VMA-Getzmann GmbH, typeAE3-M1) or some other suitable apparatus. Fine dispersion wassubsequently effected using a bead mill (for example AE3-M1 fromVMA-Getzmann) or else some other suitable dispersing assembly, withmilling being carried out with siliquartzite beads or zirconium mixedoxide beads of size d=1 mm, accompanied by cooling, until the desiredcolor strength and coloristics were obtained. Thereafter, grinding mediawere separated off, the pigment formulation was isolated andstandardized with deionized water to a concentration of about 20% anddried by means of a spray dryer from Büchi (Büchi 190). A dry powder wasobtained.

Evaluation of a Pigment Formulation

Color strength and hue were determined in accordance with DIN 55986. Theaqueous pigment dispersion and the dry powder were tested (colorstrength and compatibilities with the medium to be colored) in aconventional waterborne emulsion paint for interiors and in aconventional solventborne lacquer. The rub-out test was carried out byapplying the paint, after mixing with the pigment dispersion, to a paintcard. Subsequently, the applied coating was rubbed with the finger onthe lower part of the paint card. Incompatibility was present when therubbed area is then more strongly colored than the adjacent area notaftertreated (the rub-out test is described in DE 2 638 946).

Viscosity was determined using a cone-and-plate viscometer (RotoVisco 1) from Haake at 20° C. (titanium cone: Ø60 mm, 1°), therelationship between viscosity and shear rate in a range between 0 and200 s⁻¹ being investigated. Viscosities were measured at a shear rate of60 s⁻¹.

To evaluate the storage stability of the dispersions, viscosity wasmeasured directly after production of the formulation and also afterfour weeks' storage at 50° C.

The pigment formulation described in the example which follows wasproduced by the method described above, the following constituents beingused in the stated amounts such that 100 parts of the pigmentformulation are formed. Parts are by weight in the example whichfollows:

35 parts of C.I. Pigment Black 7 14 parts of polymer from synthesisexample 19 (table)  1 part of wetter 50 parts of water

After drying, the pigment formulation had the following composition,neglecting a residual water content of about 1%:

70 parts of C.I. Pigment Black 7 28 parts of polymer from synthesisexample 19 (table)  2 parts of wetter

The pigment formulation has a high color strength in the whitedispersion and in the lacquer and is stable. The rub-out test shows nocolor strength differences compared with the rubbed area. The dispersionproves to be readily flowable and storage stable since it is stillreadily flowable after 28 days' storage at 50° C. The dry powder isspontaneously dispersible in the waterborne white emulsion and in thesolventborne lacquer. Manual stirring is done for 3 minutes. Both colorsystems give a high color strength and also a nonflocculatingapplication free of specks. The rub-out test does not show any colorstrength differences compared to the after-rubbed area.

1. An anionically modified copolymer obtained by polymerization ofmonomers (A), (B), (C) and (D) to obtain nonionic copolymers havingreactive terminal OH groups, and subsequent conversion of the terminalOH groups to anionic end groups, wherein (A) is a monomer of formula (I)

wherein A is C₂-C₄-alkylene, B is a C₂-C₄-alkylene other than A, R ishydrogen or methyl, m is from 1 to 500; n is from 1 to 500, and the sumtotal of m+n is from 2 to 1000; (B) is a monomer of formula (II)

where D is C₃-alkylene, R is hydrogen or methyl, o is from 2 to 500; (C)is an ethylenically unsaturated monomer containing an aromatic group;and (D) is an ethylenically unsaturated monomer containing an alkylradical, wherein the copolymer is of the formulae (V) or (VI)

wherein A is C₂-C₄-alkylene, B is a C₂-C₄-alkylene other than A, D is aC₃-alkylene, m is from 1 to 500; n is from 1 to 500; and the sum totalof m+n is from 2 to 1000; o is from 2 to 500; X_(a) is an aromatic oraraliphatic radical having 3 to 30 carbon atoms optionally containingheteroatoms selected from the group consisting of N, O and S, Z_(a) is Hor (C₁-C₄)-alkyl, Z_(b) is H or (C₁-C₄)-alkyl, Z_(c) is H or(C₁-C₄)-alkyl; R is hydrogen or methyl, R¹ is hydrogen or methyl, R² ishydrogen or methyl, Y is an aliphatic hydrocarbon radical having 1 to 30carbon atoms, optionally linear or branched or cyclic, and optionallycontains heteroatoms selected from the group consisting of O, N and Sand is optionally unsaturated, W_(b) is oxygen or an NH group; X_(b) isan aromatic or araliphatic radical having 3 to 30 carbon atomsoptionally containing heteroatoms selected from the group consisting ofO, N and S, W_(a) is oxygen or an NH group, Q is SO₃, CH₂COO, PO₃M orsulfosuccinate, and M is H, a metal cation, an ammonium, an alkylatedammonium ion, or a combination thereof; a=0.001-0.9 b=0.001-0.9c=0.001-0.9 d=0.001-0.9 subject to the proviso that the sum total ofa+b+c+d is equal to
 1. 2. The copolymer as claimed in claim 1, whereinthe molar fraction of monomer (A) is 0.1 to 90%, of monomer (B) is 0.1to 90%, of monomer (C) is 0.1 to 90% and of monomer (D) is 0.1 to 90%,the molar fractions summing to 100%.
 3. The copolymer as claimed inclaim 1, wherein A is ethylene and B is propylene, or A is propylene andB is ethylene.
 4. The copolymer as claimed in claim 1, wherein thealkylene oxide units A-O)_(m) and (B—O)_(n) are in blocks.
 5. Thecopolymer as claimed in claim 1, wherein the monomer (C) is a compoundof formula (IIIa) or (IIIb)

wherein X_(a) is an aromatic or araliphatic radical having 3 to 30carbon atoms optionally containing heteroatoms selected from the groupconsisting of N, O and S, Z_(a) is H or (C₁-C₄)-alkyl, Z_(b) is H or(C₁-C₄)-alkyl, and Z_(c) is H or (C₁-C₄)-alkyl,

wherein R¹ is hydrogen or methyl, X_(b) is an aromatic or araliphaticradical having 3 to 30 carbon atoms optionally containing heteroatomsselected from the group consisting of N, O and S, W_(a) is oxygen or anNH group.
 6. The copolymer as claimed in claim 1, wherein the monomer(D) is a compound of formula (IV):

wherein R² is hydrogen or methyl, Y is an aliphatic hydrocarbyl radicalhaving 1 to 30 carbon atoms, optionally linear or branched or cyclic,and optionally contains heteroatoms selected from the group consistingof O, N and S and is optionally unsaturated, W_(b) is oxygen or an NHgroup.
 7. The copolymer as claimed in claim 1, wherein the anionic endgroups are selected from the group consisting of SO₃M, CH₂COOM, PO₃M₂and sulfosuccinate, wherein M represents H, a metal cation, NH₄ ⁺, analkylated ammonium ion or a combination thereof.
 8. A process forproducing a copolymer as claimed in claim 1, comprising the steps offree-radically polymerizing the monomers (A), (B), (C) and (D) andconverting the resulting terminal OH groups to anionic end groups.
 9. Adispersant comprising a copolymer as claimed in claim
 1. 10. Thedispersant as claimed in claim 9, wherein the dispersant is a pigmentdispersant or a filler dispersant.